Indoor Bonsai are miniature versions of tropical and semitropical trees and shrubs. Unlike temperate zone trees, which require the climactic differences between summer and winter/ day and night, the tropical-like varieties flourish in a near seasonless environment with small variations in temperature. Homes and offices do not entirely create this environment. To grow indoor Bonsai successfully, one needs to know something about their origins and life cycles in their native habitats.
Indoor Bonsai as a group are divided into two classifications. The first being true tropical species. These have a warmth requirement. Not only must it be warm, but the warmth must be somewhat constant. Temperatures should not fall below 6o degrees and should not fluctuate more than 10 degrees between night and day. The other classification is semi-tropical Bonsai. These varieties grow in their natural habitat further away from the equator than do their counterparts, the tropical varieties. The semi-tropicals enjoy a distinctive two season year. A nice warm, bright growing period, usually April thru October, followed by a bright, cooler period, usually November thru March.
Sufficient light is of vital importance for both classes. Light does not mean blazing sunshine, but brightness. Indoor Bonsai need to be protected from the mid-summer sun coming from south and west sources. If not enough light, like some winter weeks here in the Northwest, where extended periods of rain make for a succession of short, dull, dark days, artificial indoor lighting is a real plus. Indoor Bonsai can actually be grown in a dark corner away from windows if enough intensity is available with exposure at intervals of not less then 10 hours per day. Use actual "grow light" bulbs, incandescent or fluorescent are okay.
Humidity levels in Northwest homes in winter can be very low when central heating is in use. Dishes of water place near the Bonsai display are helpful. An alternative is to place the Bonsai in humidity trays that are filled with crushed rock and kept permanently filled with water. Make certain the bottoms of Bonsai containers are not touching the tray water. Regular spraying of foliage is recommended along with soil watering.
Fertilizer in the form of a water soluble mixture is easy and effective. Fertilizer should be applied at a rate that is half of what is on the label directions. A regular foliar feeding is very beneficial on a weekly basis.
Bonsai are not plants that can be neglected at any time of the year. A few minutes each day with your Bonsai will insure that all is well.